Electronically scanned array (“ESA”) antennas are commonly used in air, space and ground communication systems. These array antennas comprise multiple antenna elements whose radiation patterns are constructively combined to form antenna beams. By controlling the phase and/or amplitude of the signal fed to the individual antenna elements, the generated antenna beams are electronically shaped and scanned in a desired direction. Because the antenna beam is controlled electronically, these array antennas require minimal mechanical structure and moving parts, and are preferred for use on satellite communication systems.
The radiation pattern of an array antenna is the product of the array pattern and the radiation pattern of the individual antenna elements in the array. Desired radiation pattern characteristics, such as high directivity, low side lobes, and the absence of grating lobes, are sought after by modifying the array pattern and/or the individual antenna elements. For example, the directivity of an array antenna can be increased by increasing the aperture size of the array antenna. If a sparse array is used to obtain the larger aperture size, however, grating lobes can be generated in the radiation pattern thereby reducing the directivity of the array antenna.
Another desirable feature of array antennas is the ability to operate in multiple frequency bands and/or transmit multiple signals. For example, transmission array antennas are often required to transmit two different signals. Conventional array antennas often meet this requirement by using antenna elements designed to radiate both signals. However, when both signals pass through a twodimensional circuit within the array antenna, intermodulation products from third order mixing can cause spurious signals to appear in or near the pass-bands associated with the intended transmission signals.
It is known that a spherical array ESA is the optimal choice for ground-based satellite control antennas, because the spherical array ESA delivers excellent performance with a minimum number of antenna elements. However, the fabrication and assembly of curved array surfaces is difficult and costly. One known ESA design that approximates a spherical design is the geodesic dome antenna. A geodesic dome is an approximation of a sphere, generally made out of triangles connected by straight edges. A geodesic dome ESA provides the advantages of a spherical ESA, such as uniform beams over a hemisphere, high gain, high instantaneous bandwidth, low mismatch and polarization losses, and low life cycle costs. Thus, for example, U.S. Pat. No. 6,292,134 discloses a known ESA design that utilizes a plurality of near equilateral triangular flat panel subarrays arranged in an icosahedral geodesic dome configuration to create a faceted dome antenna.
Commonly owned U.S. Pat. No. 7,466,287, incorporated by reference herein in its entirety, discloses a sparse trifilar array antenna wherein multiple antenna elements forming an array antenna are arranged to form two-dimensional arrays approximately aligned to a triangular lattice structure. An array antenna is also disclosed having two groups of antenna elements. A first group of antenna elements is arranged in a first group of three two-dimensional arrays. A second group of antenna elements is arranged in a second group of three two-dimensional arrays. All of the antenna elements are aligned to a lattice structure with the antenna elements of each two-dimensional array being arranged in adjacent lattice positions. The first group of two-dimensional arrays is arranged to occupy lattice positions between the second group of two-dimensional arrays. The trifilar array configurations allow for multiple beam, wide angle scan coverage.
It is desirable to adapt the trifilar array antenna of U.S. Pat. No. 7,466,287 to a conformal antenna aperture to create a low cost, easily implemented conformal aperture capable of handing multiple beam, wide angle scan coverage.